In recent years, application of liquid crystal display devices to OA instruments (office automation instruments such as personal computers), portable information terminals, televisions and the like have been rapidly increased. Such a liquid crystal display device employs a color filter in order to perform color display. In general, the color filter has three primary colors of light; Red (R), Green (G) and Blue (B). The color filter is formed on a transparent substrate so that the color filter has a pattern.
Broadly known conventional production methods of the color filter are a pigment dispersion method and a staining method. The pigment dispersion method includes the steps of: (i) applying color resists on a transparent substrate; (ii) exposing the color resists to light; and (iii) developing the color resists, thereby to form a pattern of a color layer. The staining method includes the steps of: (i) applying a dying assistant on the transparent substrate; (ii) exposing the dying assistant to light; (iii) developing the dying assistant, thereby to form a pattern; and (iv) staining the pattern, thereby to obtain a color layer. However, these production methods need to repeat, for each color, each process of washing, applying, exposing and developing. Thus, simplification of the process is difficult. Further, spin coating in the step of applying increases an amount of material loss.
Other production methods of a color filter other than the above-mentioned are, e.g. an electrodeposition method, a printing method, and other methods. The electrodeposition method forms a transparent electrode pattern on a transparent substrate and carries out electro-deposition by supplying electricity to the transparent electrode while soaking the transparent substrate in respective electrolytes of respective colors. The printing method forms a color layer by printing each color on a transparent substrate. However, the electrodeposition method has a problem in that the pattern that can be formed by this method is limited. The printing method also has a problem in that it is difficult to form a very fine pattern.
In contrast to each of the color filter production method mentioned above, an inkjet method does not need an exposure process and a development process because in the inkjet method a pattern is formed directly by discharging (i.e. jetting out) ink onto the transparent substrate from an inkjet head moving over the transparent substrate. Accordingly, because the inkjet method makes it possible to reduce cost by reducing an amount of the ink to use and simplifying the process, the inkjet method currently draws attention as a color filter production method. In the inkjet method, the formation of the color layer by the discharging of the ink is carried out in various ways. For example, the ink is jetted out into a plurality of concave sections surrounded by divider members provided on the transparent substrate. In an other case, for example, a water repellent pattern region and a hydrophilic pattern region are provided on the transparent substrate in advance of the discharging of the ink, so that a color layer that has a precise pattern is formed by discharging the ink. Furthermore, in still an other case, the ink is jetted onto a display section after an amount of a jetted-out droplet and a landing position of the droplet is stabilized by preliminarily discharging the ink onto a non-display section which will not be used for displaying. (For example, Japanese Laid-Open Patent Application Publication 1995/318723 ((Tokukaihei 7-318723, published on Dec. 8, 1995): hereinafter, referred to as Patent Document 1)
Other documents describing conventional arts are as follows:
Japanese Laid-Open Patent Application Publication 2002/250811 ((Tokukai 2002-250811, published on Sep. 9, 2002) hereinafter, referred to as Patent Document 2);
Japanese Laid-Open Patent Application Publication 2003/21714 ((Tokukai 2003-21714, published on Jan. 24, 2003): hereinafter, referred to as Patent Document 3);
Japanese Laid-Open Patent Application Publication 1997/101411 ((Tokukaihei 9-101411, published on Apr. 15, 1997): hereinafter, referred to as Patent Document 4);
Japanese Laid-Open Patent Application Publication 1997/21910 ((Tokukaihei 9-21910, published on Jan. 21, 1997): hereinafter, referred to as Patent Document 5);
Japanese Laid-Open Patent Application Publication 1996/304619 ((Tokukaihei 8-304619, published on Nov. 22, 1996): hereinafter, referred to as Patent Document 6);
Japanese Laid-Open Patent Application Publication 1998/123310 ((Tokukaihei 10-123310, published on May 15, 1998): hereinafter, referred to as Patent Document 7); and
Hyoumen Kagaku, Vol. 24, No. 2, pp. 90-97, 2003: hereinafter, referred to as Non-Patent Document 1).
However, the color filter production using the inkjet method has a problem in that the ink, which has landed on the transparent substrate, is dried hardly with an even film thickness all over the display section. This results in uneven distribution of the ink, as explained as follows.
FIG. 6 is a sectional view of a color filter. FIG. 6 illustrates a color filter production process using a conventional inkjet method. In the color filter production process using conventional inkjet method, the color filter is formed by discharging ink 103 out so that the ink 103 lands on a substrate 101, on which a black matrix 102 is formed.
The ink 103 used in the inkjet method needs to spread all over a hydrophilic part of the substrate 101, after the ink 103 lands on the substrate 101 on which a black matrix 102 is formed. Thus, not low viscosity ink but ink of high fluidity is generally used as the ink 103. If the ink 103 landed on a picture element region was leaked into another adjacent picture element region, the leakage would cause color mixing, the picture element regions separated by the black matrix 102. The black matrix 102 normally has water repellent property in order to prevent the leakage. In this case, the ink 103 that has landed on a predetermined picture element on the substrate 101 forms a convex shape whose midsection has a large thickness in the picture element region. When the color filter is completed by drying the ink 103, the dried ink 103 keeps the convex shape that it has right after the landing.
In the case where the ink (that is, a color layer) has a convex shape on the above color filter as described above, various problems occur, which do not occur in a color filter whose color layer is formed with an even thickness. The various problems are: uneven cell thickness, diminishment of color in a vicinity of the black matrix, uneven distribution of color deepness in the picture element region and the like.
In the above Patent Documents 1 through 3, the shape of the ink layer formed in each picture element region is not specifically described. In the Patent Document 5, although it is described that the ink dried on the substrate forms a convex shape, a problem resulting from this shape of the ink and a method of solving the problem are not disclosed.
In Patent Documents 6 and 7, exemplary methods for compensating the convex shape of the ink are disclosed. The method proposed in Patent Document 6 is a method according to which negative-type photo-curing resin is applied onto a color filter including a convex-shaped ink layer and then exposed to light incident thereon from above a backside of the color filter. In this way, a convex section level of the color filter is leveled off spontaneously. The method proposed in Patent Document 7 is a method according to which, after forming the ink layer on the substrate by the inkjet method firstly, a black matrix is formed by a photo-lithography process.
By the method proposed in Patent Document 6, a convex section level is evened (leveled off). However, because the another problem, that is, the problem in which the ink thickness close to the black matrix becomes thin, cannot be solved, uneven distribution of color deepness cannot be dissolved. The diminishment of the color in the vicinity of the black matrix is also left unsolved.
According to the method proposed in Patent Document 7, the ink layer is formed directly on the glass substrate by the use of the inkjet method. When forming the ink layer, the black matrix that serves a bank is not provided. Accordingly, the problem such as the color diminishment close to the black matrix does not occur. However, because accurate formation of each section of the colors is difficult in consideration of precision of landing an ink droplet, and the other factor, it becomes further difficult to apply this method to formation of a color filter of a very fine pattern.